The S.I unit of moment of a force is

1. Analyze the question

The question asks for the Standard International (S.I.) unit of the moment of a force.

2. Explain the concept

In physics, the moment of a force (also known as torque) is defined as the product of the force applied and the perpendicular distance from the pivot (or fulcrum) to the line of action of the force.

The mathematical formula is:

• The S.I. unit of Force is the Newton (N).
• The S.I. unit of Distance is the meter (m).

Therefore, the unit of the moment of a force is the product of these two units.

3. Show the solution

• Step 1: Identify the formula: $\text{Moment} = F \times d$
• Step 2: Substitute the S.I. units: $\text{Unit} = \text{Newton} \times \text{meter}$
• Step 3: Combine the units: $\text{Unit} = \text{Nm}$

While the Joule (J) is also a unit of energy (Force $\times$ distance), the standard convention for expressing the moment of a force is Newton-meter (Nm) to distinguish it from energy.

4. Identify the answer

Comparing our result (Nm) with the given options: A. kgm B. Nm C. Jm D. µm$^{-1}$

The correct option is B.

5. Tip

Don't confuse the Newton-meter (Nm) for a moment with the Joule (J) for work or energy. Even though they have the same dimensional formula ($ML^2T^{-2}$), we use Nm for moments to indicate that the force is applied perpendicularly to a distance, whereas Joules are used when force causes displacement in the direction of the force.